Camelot said: ‘Of our 9.5 million registered online players, we believe that around 26,500 players’ accounts were accessed. A much smaller number – fewer than 50 – have had some activity take place within the account since it was accessed.’

However, they added that there had been ‘no unauthorised access to core National Lottery systems or any of our databases, which would affect National Lottery draws or payment of prizes.’

Camelot said that no money had been taken from or added to people’s accounts and they are now investigating what happened.

They added that they do not hold players’ debit card or bank account details.

A statement on the Camelot website added: ‘A much smaller number – fewer than 50 – have had some activity take place within the account since it was accessed. This was limited to some of their personal details being changed – and some of these details may have been changed by the players themselves.

‘However, we have taken the measure of suspending the accounts of these players and are in the process of contacting them to help them re-activate their accounts securely.’

They have reported the breach to the National Crime Agency and the National Cyber Security Centre.